In the field of toners for electrophotography, with the progress of electrophotographic systems, it has been demanded to develop toners adaptable for high image quality and high copying speed.
From the viewpoint of high image quality, in order to well control or reduce a particle size of the toner, it is known that the toner is produced by an aggregating and unifying method (aggregation/fusion method) in which fine resin particles and the like are aggregated and fused together in an aqueous medium.
For example, Patent Document 1 discloses a process for producing a toner for developing electrostatic images which contains at least a crystalline polyester resin and a colorant and has a specific dielectric loss factor for the purpose of improving a low-temperature fixing property, a high-density image forming property and an anti-fogging property thereof. The production process of Patent Document 1 includes an aggregated particle-forming step of mixing a dispersion of resin particles prepared by dispersing binder resin particles containing a crystalline polyester resin in a dispersing medium with a colorant dispersion prepared by dispersing a colorant in a dispersing medium and then adding an aggregating agent to the resulting mixed dispersion to form aggregated particles, and a fusing and unifying step of heating the aggregated particles to fuse and unify the particles while adding an acid and a surfactant thereto.
Patent Document 2 discloses a process for producing a developer which includes a step of adding an aggregating agent to a dispersion containing a binder resin and colorant-containing fine particles to aggregate the fine particles with the binder resin, and a step of fusing the resulting aggregated particles together to form toner particles, for the purpose of attaining a high image quality and producing a developer having a good particle size distribution. In the production process, a pH value of the dispersion before adding the aggregating agent thereto, a pH value of the dispersion after adding the aggregating agent thereto and a pH value of the dispersion after the fusion are controlled to satisfy a specific relationship with each other.
Patent Document 3 discloses a process for producing a toner for electrophotography which includes a step of emulsifying a binder resin containing a polyester in an aqueous medium, a step of aggregating emulsified particles in the resulting emulsion at a temperature not higher than a “glass transition point of binder resin+20° C.”, a step of terminating aggregation of the emulsified particles by adding a salt of an alkylethersulfate or a salt of an alkylsulfate thereto, and a step of heating the aggregated particles at a specific temperature to unify the particles, for the purpose of obtaining toner particles having a high circularity.
Patent Document 4 discloses a toner for electrophotography which is produced by a process including a step of emulsifying a raw polyester containing amorphous polyester containing a constitutional unit derived from a trivalent or higher-valent carboxylic acid in an amount of from 2.0 to 12.0 mol % and a crystalline polyester in an aqueous medium, or a step of mixing the raw polyester with an organic solvent and then adding the aqueous medium to the resulting mixture to emulsify the raw polyester therein, thereby obtaining a dispersion of polyester particles, and a step of subjecting the dispersion of polyester particles to aggregation and unification, for the purpose of improving a low-temperature fixing property and an anti-hot offset property of the toner.
Patent Document 5 discloses a process for producing a toner which includes a step of subjecting a dispersion of toner particles containing core particles produced by aggregating resin particles, pigment particles and wax particles to reslurry washing treatment with an alkali solution having a pH of 8 to 12, and a step of subjecting the dispersion of the toner particles to reslurry washing treatment with an acid solution having a pH of 2 to 6 wherein the process further includes a flow-through water-washing treatment step with the acid solution and a flow-through water-washing treatment step with the alkali solution between the above reslurry washing treatment steps, for the purpose of increasing a life of the toner and preventing occurrence of lacks in toner images or toner cloud upon transfer of the toner.
Patent Document 6 discloses a process for producing a toner for developing electrostatic images in which a ratio between an amount of Na ions on a surface of smaller-diameter particles of the toner and an amount of Na ions on a surface of larger-diameter particles of the toner satisfies a specific relationship, for the purpose of improving a tribocharging property of the toner and efficiently removing discharge products deposited on a surface of an image-bearing member. The production process of Patent Document 6 includes a step of washing the toner with a treating solution having a pH of not less than 9 and not more than 10, a step of adjusting a pH of the toner to 4 or less and then washing the toner while being treated with an ultrasonic wave, and a step of washing the toner with ion-exchanged water.
Patent Document 7 discloses a process for producing a toner for electrophotography which includes a step of obtaining a dispersion of toner particles containing a polyester in an aqueous medium in the presence of a surfactant and a step of washing the resulting toner particles with an alcohol aqueous solution containing an alcohol having 1 to 5 carbon atoms in an amount of not less than 0.1% by weight and less than 5% by weight, for the purpose of improving a storage stability and a developability of the toner.